The present invention relates to a regenerative braking system for a car, and particularly to a regenerative braking system for a car wherein the decelerating energy of the car is captured and used for the starting/accelerating energy.
In a PTO (Power-take-off) output unit (system) or a deceleration energy recovery system as conventionally known, a part of the kinetic energy dissipated mainly as heat at a brake or engine during the deceleration of a car, is captured in the form of hydraulic operating oil and accumulated in an accumulator. The accumulated energy is utilized for the starting energy and accelerating energy of the car.
For example, in 1976 C. J. Lorence Corporation in England announced the development of such a system using a bus of British Leyland Corporation. Since then, various research and development has been conducted in Europe.
Recently, Japanese Patent Application Laid-open Nos. 62-15128, 62-37215, 62-39327 etc. have disclosed a deceleration energy recovery system which is essentially formed of a transmission (hereinafter referred to as T/M), a multi-stage gear-changed PTO unit, a PTO output shaft, a pump/motor, a hydraulic oil circuit, an electromagnetic clutch, an accumulator, and a control unit.
The T/M includes a counter shaft driven through an engine clutch, a main shaft connected to a wheel driving line, and a multi-staged gear train mechanism transferring the rotation of the counter shaft to the main shaft through the gears. The multi-stage gear-changed PTO unit includes a counter shaft PTO gear disconnectably coupled to the counter shaft through a counter shaft PTO gear synchronizer, a main shaft PTO gear coupled to the counter shaft PTO gear and disconnectably coupled to the main shaft through a main shaft PTO gear synchronizer, and a PTO output shaft driven through driving gears coupled to the main shaft PTO gear. The pump/motor is coupled to the PTO output shaft. The hydraulic oil circuit includes a high pressure oil line and a low pressure oil line and serves to connect the accumulator to an oil tank through the pump/motor, and the electromagnetic clutch serves to connect/disconnect the oil circuit to/from the PTO shaft.
The control unit controls the electromagnetic clutch and works the pump/motor as either a pump or a motor in response to the running condition of the car. Namely, for working the pump/motor as a pump, the torque of the wheels during the decelerating mode serves to accumulate the operating oil into the accumulator through the PTO unit to capture the kinetic energy (i.e. braking energy mainly lost as heat in the brake or engine. For working the pump/motor as a motor, the operating oil accumulated in the accumulator serves to generate starting/accelerating torque to drive the wheels through the PTO unit.
The control manner of this control unit is as follows:
1 When the car starts with the inner pressure of the accumulator being sufficient, the pump/motor is controlled to serve as a variable capacity type motor, the capacity of which is controlled by varying the displacement angle (incline angle) of the swash plate or shaft in response to the accelerator pedal positions.
Since the pump/motor is also connected to the electromagnetic clutch, when the electromagnetic clutch is coupled to the PTO unit by the control unit, the pump/motor drives the car based on the hydraulic power accumulated in the oil circuit.
In the meantime, when the car speed exceeds a preset value corresponding to the gear position selected by a driver, the engine clutch is coupled to the engine for the engine cruising. At the same time the PTO unit is gearchanged so as to turn off the counter shaft synchronizer which was on and turn on the main shaft synchronizer which was off, and the combined cruising of the pump/motor with the engine is carried out according to the hydraulic power based on the pedal position only if the accelerator pedal is largely operated by the foot.
2 During the braking mode, the electromagnetic clutch is made on, and the displacement angle control signal (pump capacity control signal) according to the brake pedal position is supplied to the pump/motor for the corresponding pumping operation, while at the same time the engine is declutched.
Thus, the control unit controls the engine clutch to decouple the engine from the driving line of the wheels in order to capture a part of the braking energy which is to be consumed in the engine during the braking mode and to relieve the captured energy during the accelerating mode, while coupling the engine to the driving line in order to use the engine power alone or in combination with the motor during the starting/accelerating mode.
In such a prior art system, since the braking operation by the hydraulic power is not performed unless the brake pedal is operated by the foot, it is disadvantageous that the car cannot be braked by the hydraulic power in the same manner when a conventional exhaust brake is applied.
Also since the engine braking is used in combination with the hydraulic braking after the rotational speed of the engine has been increased up to the synchronous engine speed with the engine clutch being off when the brake pedal is restored, it is disadvantageous that braking energy dissipated as heat in the engine when the car is cruising in the engine braking mode, cannot be sufficiently recovered.